Add additional class conditions for JTA auto-configuration

Previously, JTA auto-configuration would fail with a variety of
ClassNotFoundExceptions and NoClassDefFoundErrors if it was used with
an “incomplete” classpath. This commit adds a number of classes to
@ConditionalOnClass annotations so that the auto-configuration backs
off gracefully in the absence of certain classes.

Specifically, the following now work as expected:

 - Deploying an app to a server with JTA available via JNDI when the
   app does not use transactions
 - Auto-configuration of Atomikos without JMS
 - Auto-configuration of Bitronix without JMS

Both XADataSourceAutoConfiguration and JndiDataSourceAutoConfiguration
have been updated to back off in the absence of spring-jdbc; a
dependency of DataSourceProperties which is used by both classes.

Error handling in AtomikosDependsOnBeanFactoryPostProcessor and
BitronixDependentBeanFactoryPostProcessor has been enhanced so that the
correct dependencies are established, even in the absence of JMS.

Fixes gh-1538